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Each dot represents data from one animal (grade 0: n = 14; grade 1: n = 11; grade 2: n = 7; and grade 3: n = 9). Data represent the mean (± 95% confidence). The unpaired t‐test was used to verify the statistical significance. Grade 0 versus grade 1: P = 6.80E‐11; grade 1 versus grade 2: P = 0.0007; and grade 2 versus grade 3 P = 0.0086.
